1. Field of the Invention
The present invention is a method of capping with a high compressive stress oxide, a boron phospho-silicate glass (BPSG) interlayer dielectric (ILD) gapfill that has been deposited on a topographic silicon substrate, in order to eliminate the formation of cracks in subsequently deposited silicon nitride (SiN) layers, other subsequently deposited high tensile stress layers and cracks that result from other post-BPSG deposition high temperature processes.
2. Description of the Related Art
The shrinkage of device sizes in ULSI circuit fabrications has led to the widespread use of self-alignment contacts (SAC) and multilayer structures in order to exceed the existing tolerance limits imposed by photolithography and etching processes (see C. Y. Chang and S. M. Sze, "ULSI Technology," McGraw-Hill Co., New York, 1996, pp 487-488). Said shrinkage of device sizes has also dictated the use of boron phospho-silicate glass (BPSG) as an interlayer dielectric (ILD) of choice because of its superior gapfilling of narrow spaces and for flow characteristics that lead to smooth coverings of complex topographies. The use of BPSG as both an insulating and planarizing layer is discussed by Lee et al (U.S. Pat. No. 5,354,387).
The same flow properties of BPSG which are so beneficial for gapfilling and smooth coverage, lead to problems with crack formation when high temperature post-deposition processes are carried out. In particular, subsequent depositions of LP-SiN layers, common in ULSI circuit fabrications using self-alignment contacts, show significant cracking. Cracks also appear as a result of subsequent depositions of other high tensile stress films and as a result of other high temperature processing steps, such as anneals or rapid thermal oxidation (RTO) processes. It has been recognized that BPSG layers can be protected by the application of surface films (see Hayashi, U.S. Pat. No. 5,688,720), but the use of such films has not been applied to eliminate the SiN cracking problem associated with post-deposition high temperature processing.